Chapter 9. Earthquakes
Exercises on Earthquakes
Adapted by Joyce M. McBeth, Sean W. Lacey, Tim C. Prokopiuk (2018) University of Saskatchewan from Deline B, Harris R, & Tefend K. (2015) “Laboratory Manual for Introductory Geology”. First Edition. Chapter 13 “Earthquakes” by Randa Harris, CC BY-SA 4.0. View Source. Last edited: 23 Mar 2020
Name: _______________
NSID and student number: ____________
Date and lab section time: _____________
TAs’ names: _______________
Please hand in this lab to your TAs at the end of the lab period.
9-E1 LAB EXERCISE – LOCATING AN EPICENTER
You will determine the location of an earthquake epicenter using seismograms from Carrier, Oklahoma, Smith Ranch in Marlow, Oklahoma, and Bolivar, Missouri. These are actual seismograms that you will be reading, from an actual earthquake event. For each seismogram, three different readouts are given, because the seismograph measured movement along three different axes simultaneously. You can use any of the three readouts for each station in your calculations, because each of the readouts will have the same arrival time for the different components of each wave.
First, determine the time when the P and S waves first arrived for each station. To identify the P and S waves, refer to the illustrations in the overview section of this chapter. Look for a pattern change as the amplitude of the lines gets bigger; this indicates the arrival of each of the waves. Mark both the arrival of the P-wave and S-wave on the seismogram, then using the time scale in seconds, determine the time difference between the P and S wave first arrivals. Write these times in Table 9.1 below for each of the three seismograms. (12 pts).
The difference between the P and S wave first arrivals will be used to determine the distances to the epicenter from each station in Figure 9-E4. Use Figure 9.11 from the overview section of this lab (replicated below) to determine the distance of the epicenter from each station. Make sure that you use the curve for the difference between the S and P wave first arrival times (S-P). Find the difference between the S and P first arrival times in seconds on the y-axis, draw a line over to the S-P curve at the same time, then draw a line down to the x- axis to determine the distance. Add the values to Table 9.1 above.
Figure 9-E4 is a map showing the three stations on it. Next, you will draw circles on this map to represent the distance of the earthquake epicenter from each station. This map includes a legend in kilometers. For each station, note the distance to the epicenter. Measure the scale on the map in Figure 9-E4 in centimeters and convert your distances in kilometers to centimeters (e.g., if the map’s scale of 100 km = 2.1 cm on your ruler, and you had a measured distance from one station of 400 km, that would equal 8.4 cm on your ruler). For this fictional example, you would use a drafting compass to make a circle around the station that is 8.4 cm in radius (from the centr